The preparation of a thermosettable vinyl ester resin by the reaction of an unsaturated monocarboxylic acid such as methacrylic acid with a polyepoxide is known. While the physical properties of the cured resin can be varied depending on the choice of reactants, the choice of monomer copolymerizable with the resin and the like, the properties may also be modified by adding various materials to the resin. Inert reinforcing materials such as glass fibers and inert fillers such as CaCO.sub.3 or kaolin clay are commonly employed both to improve properties and to reduce costs.
A variety of other additives are also known: thickening agents, thermoplastic low profile (smooth surface) additives, rubbery polymers to improve impact resistance, and the like. However, compatibility of these additives with the resin may frequently be a major problem which calls for other additives to stabilize the system. Some of the additives, unfortunately, are also susceptible to removal from the cured resin by contact with solvents and the like. Consequently, the advantages of certain additives may be lost or diminished in value because of these problems.
It would be desirable to have a thermosettable resin that inherently provides all of the desired properties. This ideal may never be reached but an object of this invention is to inherently provide improved impact resistance in the vinyl ester resin by chemically incorporating a polydiene rubber into the thermosettable resin itself. Other objects, benefits and advantages of the invention will become readily apparent from the description which follows.